This invention relates to a catalytic reforming process using zeolite catalysts. Catalytic reforming is a process for treating naphtha fractions of petroleum distillates to improve their octane rating by producing aromatic components and isomerizing normal paraffins to isoparaffins from components present in naphtha feedstocks. Included among the hydrocarbon reactions occurring in reforming processes are: dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to aromatics, and hydrocracking of paraffins to lighter gases with a lower boiling point than gasoline. Hydrocracking reactions which produce light paraffin gases are not desirable as they reduce the yield of products in the gasoline boiling range.
Natural and synthetic zeolitic crystalline aluminosilicates containing Group VIII metals and Groups IA and IIA metal cations exhibit catalytic properties for various types of hydrocarbon conversions including catalytic reforming.
U.S. Pat. No. 4,789,656 issued to Chen et al. discloses a process for synthesizing Beta Zeolite catalyst. A noble metal component is incorporated into the beta zeolite catalyst. Noble metals which are incorporated within the zeolite include metals of Groups IB, IIB, VA, VIA or VIIIA.
U.S. Pat. No. 4,652,360 issued to Dessau discloses a reforming process using ZSM-5 and ZSM-11 zeolite catalysts having a silica to alumina ratio of at least 12 containing a Group VIII metal. The zeolite is base exchanged with Group IA metal cations.
U.S. Pat. No. 4,835,336 issued to McCullen discloses a process for converting a C.sub.6 -C.sub.12 paraffinic hydrocarbon feed to aromatics with a noble metal, low activity medium pore size zeolite catalyst including a beta zeolite catalyst.
U.S. Pat. No. 4,867,864 issued to Dessau discloses a reforming process using a non-acidic beta zeolite catalyst composition containing a Group VIII metal. The acidity of the catalyst is reduced by treating it with a solution containing Group IA or Group IIA metal cations.
U.S. Pat. No. 4,927,525 issued to Chu discloses catalytic reforming processes with improved zeolite catalysts. This reference discloses the use of beta zeolite in reforming processes. The beta zeolite described in this reference contains a noble metal and an alkali metal. The noble metal is selected from the group consisting of platinum, iridium, osmium, palladium, rhodium and ruthenium. The alkali metal is selected from the group consisting of lithium, sodium, potassium and rubidium.
The effect of alkali metal loading on catalytic activity is shown in Examples 7-11 of U.S. Pat. No. 4,927,525. These examples show that certain zeolitic catalysts which have a Li.sup.+ :AlO.sub.2.sup.- ratio of less than 1 are inferior to zeolitic catalysts which have Li.sup.+ :AlO.sub.2.sup.- ratios greater than 1. Therefore, this reference teaches that by lowering the ratio of AlO.sub.2 :Li to less than 1, the catalytic reforming properties of these materials are improved.
I have found that the catalytic reforming properties of the beta zeolite catalyst and other large-pore zeolites are significantly improved when the molar ratio of aluminum to Group IA or Group IIA metal cations is between about 1.0 and 4.0. These properties include high catalyst stability at low pressure, high catalyst activity, and lower methane and ethane production.